DETERMINATION OF FLUORESCENCE POLARIZATION OF DOUBLE CHROMOPHORE COMPLEXES

Polarized fluorescence of rigid double-chromophore complexes with intracomplex energy exchange between chromophores was analyzed, and the formula for the degree of polarization derived for the case of steady-state excitation: P = (3 cos(2) theta - 1 + 2A)/(3 + cos(2) theta + 4A). In this formula theta is the angle between the transition dipole moments of chromophores in complexes, and A is the parameter dependent on the spectroscopic features of chromophores and energy migration rates. The case of excitation by a delta-pulse was also analyzed, and a formula for fluorescence polarization kinetics was derived. As an example of the application of the derived formulae, the polarized fluorescence spectra and their picosecond kinetics were calculated for the beta-subunits of the blue-green algae Agmenellum quadruplicatum. The results obtained were compared with experimental measurements of Mimuro et al. (1986, Biochim. Biophys. Acta 848, 155-166) and found to match these data well.